1. Field of the Invention
The present invention relates, generally, to compression spray applicators for coating fluids and, more especially, to manually-operated spray applicators which may be used to apply surface coating of viscous fluids such as plaster or other texturizing materials.
2. Description of the Background Art
Compression sprayers are, of course, well known. Generally, a jet of compressed air is employed to pressurize a source of fluid which is propelled as the result of that pressure head, to entrain the fluid either directly or indirectly (e.g., venturi), or simply to propel the fluid by direct impingement on it.
U.S. Pat. No. 2,923,481 is generally representative of the overall configuration of a manually-operated compression sprayer used, for example, to apply household and garden spray solutions for controlling pests, deodorizing, or the like. While that patent is more particularly directed to a specific nozzle configuration within such a context, it exemplifies a construction where a closed compression chamber receives a pressurizing piston which, upon manual stroking, creates a pressure head responsible for propelling liquid housed within an associated reservoir. As the concept behind these household or garden sprayers is now quite notorious, further details in respect thereof are not warranted herein.
More to the direct point of the present invention, the principles behind the compressive spray application of fluids have been adapted for spray applicators designed expressly for the application of very viscous materials, such as plaster or viscous paint materials used to provide a "texurized" surface. However, when the focus shifts from relatively low viscosity fluids, such as a liquid deodorant or insecticide material, to the application of these more viscous surface coatings, the approaches heretofore proposed have generally centered upon spray applicators employing a source of pressurized air or other propellant gas. Only scant attention has been paid to designs for a manually-operated compression sprayer useful in this context. For example, U.S. Pat. No. 4,204,645 discloses a relatively conventional compression sprayer equipped with a special head permitting spray application of, inter alia, viscous fluids which might include plaster or the like.
By way of further general background, there is a particularly vexing problem associated with compression spray applicators and one exacerbated when dealing with those designated for the application of plaster or similar materials. When the spray procedure first begins, and oftentimes at its termination, there is a pronounced tendency for a surge of fluid vis-a-vis the propelling airjet. This results in a highly undesirable spattering (i.e., "dribbling") during those times when the applicator is operating under other than steady state conditions as the fluid is improperly or incompletely atomized or propelled by the airjet.
Turning directly to representative patents concerning structures for spray applicators which are designed to prevent or minimize this spattering, whether in the spraying of paint or more viscous materials such as plaster, U.S. Pat. No. 1,609,465 is illustrative. That device is a paint sprayer where paint is supplied to a "spray gun" through a first passageway and pressurized air through another. When an operating trigger is depressed, a portion of the pressurized air activates a diaphragm which is moved rearwardly against the force of a biasing spring maintaining a valve member in a normally closed position. As the valve member moves rearwardly it opens the spray nozzle so paint can flow from a reservoir into the airstream. The patentee provides for the issuance of propelling air through the nozzle for a very slight time period immediately prior to movement of the diaphragm and likewise causes the air to flow for a slight time period after the force on the diagram is released, to ensure that all of the paint is atomized and thereby prevent unwanted spattering. The diaphragm is pressure-responsive and is caused to open as the pressure builds once the trigger is pulled and then to close as the pressure drops once the trigger is released. Thus, since the rise and fall of pressure are not instantaneous, this approach relies on the slope of the pressure gradient at the beginning and ending of the spraying sequence to achieve the aforementioned objective.
A somewhat similar arrangement is disclosed in U.S. Pat. No. 1,332,554. The patentee there describes a spray gun useful for depositing paints or other coatings which might include a solid particulate in powder form. Like the structure described above, air is admitted to the device through one passageway and the fluid via another passageway. The two routes converge near the tip where fluid resides in an annular chamber surrounding a stem through which the pressurized air passes. The stem is initially sealed against the discharge port of that annular chamber and, upon activation of the device, is retracted out of engagement therewith so that the fluid may be propelled by the pressurized airjet. This occurs upon movement of an operating handle which causes the rear part of a piston to be exposed to atmospheric pressure whereby the pressure gradient causes the entire stem to retract in the manner noted above.
Conceptually similar approaches have been applied to the task of dispensing plaster or other viscous coatings from a spray gun. Illustrative of such devices are those disclosed in U.S. Pat. No. 2,801,880, No. 2,964,302, and No. 3,236,459. In each of those structures, the driving force for application of the plaster is compressed air which is admitted to the spray gun for the purpose of propelling plaster admitted from a container associated with the gun.
These prior art attempts to provide apparatus for the application of plaster or similar viscous coating fluids, centering upon adaptations of paint sprayers or the like which rely upon a source of compressed air for the driving force, leave much to be desired from the perspective of a "nonprofessional," such as an individual homeowner wishing to undertake his own home improvements. Not only is the gun applicator usually a fairly complicated and expensive device, one necessarily must have an air compressor to drive the gun thereby further increasing the cost. The capital expense of acquiring such a device for spray application of plaster or the like puts many of these applicators well beyond the financial reach of most individuals. Apart from costs, the use of a spray gun and associated compressor can complicate the coating procedure since these devices tend to be bulky; the reach is limited by the length of tubing between the compressor and spray gun; and the entire package must be moved from room to room throughout a building, sometimes at considerable inconvenience. Thus, the convenience of simply pulling a trigger on the spray gun applicator is paid for by the loss of portable mobility. Further along these lines, large spray apparatus of this type require a fairly lengthy period of personal familiarization in order to obtain satisfactory results which, from an individual homeowner's point of view, leads to at least two further problems--the first time the apparatus is used it may be found by many to be a somewhat intimidating experience due to the noise and power of the device and, by the time one becomes accustomed to, or familiar with, the device, the project prompting its use may well be completed.
It should also be appreciated that even "professionals" sometimes find the use of unweildy compressor/spray gun apparatus very undesirable. Small jobs or small contractors' operations oftentimes do not justify, from either a convenience or economic perspective, the use of such devices.
Accordingly, the need exists to provide a spray applicator for spraying viscous fluid coatings such as plaster or other texturizing materials which is simple in construction and use and which nonetheless is durable and reliable. The need also exists to provide such a device at a reduced cost so that the same may be procured and used by individual home owners.